/* SPDX-License-Identifier: GPL-2.0 */
#ifndef _BLK_CGROUP_H
#define _BLK_CGROUP_H
/*
 * Common Block IO controller cgroup interface
 *
 * Based on ideas and code from CFQ, CFS and BFQ:
 * Copyright (C) 2003 Jens Axboe <axboe@kernel.dk>
 *
 * Copyright (C) 2008 Fabio Checconi <fabio@gandalf.sssup.it>
 *                    Paolo Valente <paolo.valente@unimore.it>
 *
 * Copyright (C) 2009 Vivek Goyal <vgoyal@redhat.com>
 *                    Nauman Rafique <nauman@google.com>
 */

#include <linux/cgroup.h>
#include <linux/percpu.h>
#include <linux/percpu_counter.h>
#include <linux/u64_stats_sync.h>
#include <linux/seq_file.h>
#include <linux/radix-tree.h>
#include <linux/blkdev.h>
#include <linux/atomic.h>
#include <linux/kthread.h>
#include <linux/fs.h>

/* percpu_counter batch for blkg_[rw]stats, per-cpu drift doesn't matter */
#define BLKG_STAT_CPU_BATCH     (INT_MAX / 2)

/* Max limits for throttle policy */
#define THROTL_IOPS_MAX         UINT_MAX
#define FC_APPID_LEN              129


#ifdef CONFIG_BLK_CGROUP

enum blkg_iostat_type {
        BLKG_IOSTAT_READ,
        BLKG_IOSTAT_WRITE,
        BLKG_IOSTAT_DISCARD,

        BLKG_IOSTAT_NR,
};

struct blkcg_gq;

struct blkcg {
        struct cgroup_subsys_state      css;
        spinlock_t                      lock;
        refcount_t                      online_pin;

        struct radix_tree_root          blkg_tree;
        struct blkcg_gq __rcu           *blkg_hint;
        struct hlist_head               blkg_list;

        struct blkcg_policy_data        *cpd[BLKCG_MAX_POLS];

        struct list_head                all_blkcgs_node;
#ifdef CONFIG_BLK_CGROUP_FC_APPID
        char                            fc_app_id[FC_APPID_LEN];
#endif
#ifdef CONFIG_CGROUP_WRITEBACK
        struct list_head                cgwb_list;
#endif
};

struct blkg_iostat {
        u64                             bytes[BLKG_IOSTAT_NR];
        u64                             ios[BLKG_IOSTAT_NR];
};

struct blkg_iostat_set {
        struct u64_stats_sync           sync;
        struct blkg_iostat              cur;
        struct blkg_iostat              last;
};

/*
 * A blkcg_gq (blkg) is association between a block cgroup (blkcg) and a
 * request_queue (q).  This is used by blkcg policies which need to track
 * information per blkcg - q pair.
 *
 * There can be multiple active blkcg policies and each blkg:policy pair is
 * represented by a blkg_policy_data which is allocated and freed by each
 * policy's pd_alloc/free_fn() methods.  A policy can allocate private data
 * area by allocating larger data structure which embeds blkg_policy_data
 * at the beginning.
 */
struct blkg_policy_data {
        /* the blkg and policy id this per-policy data belongs to */
        struct blkcg_gq                 *blkg;
        int                             plid;
};

/*
 * Policies that need to keep per-blkcg data which is independent from any
 * request_queue associated to it should implement cpd_alloc/free_fn()
 * methods.  A policy can allocate private data area by allocating larger
 * data structure which embeds blkcg_policy_data at the beginning.
 * cpd_init() is invoked to let each policy handle per-blkcg data.
 */
struct blkcg_policy_data {
        /* the blkcg and policy id this per-policy data belongs to */
        struct blkcg                    *blkcg;
        int                             plid;
};

/* association between a blk cgroup and a request queue */
struct blkcg_gq {
        /* Pointer to the associated request_queue */
        struct request_queue            *q;
        struct list_head                q_node;
        struct hlist_node               blkcg_node;
        struct blkcg                    *blkcg;

        /* all non-root blkcg_gq's are guaranteed to have access to parent */
        struct blkcg_gq                 *parent;

        /* reference count */
        struct percpu_ref               refcnt;

        /* is this blkg online? protected by both blkcg and q locks */
        bool                            online;

        struct blkg_iostat_set __percpu *iostat_cpu;
        struct blkg_iostat_set          iostat;

        struct blkg_policy_data         *pd[BLKCG_MAX_POLS];

        spinlock_t                      async_bio_lock;
        struct bio_list                 async_bios;
        struct work_struct              async_bio_work;

        atomic_t                        use_delay;
        atomic64_t                      delay_nsec;
        atomic64_t                      delay_start;
        u64                             last_delay;
        int                             last_use;

        struct rcu_head                 rcu_head;
};

typedef struct blkcg_policy_data *(blkcg_pol_alloc_cpd_fn)(gfp_t gfp);
typedef void (blkcg_pol_init_cpd_fn)(struct blkcg_policy_data *cpd);
typedef void (blkcg_pol_free_cpd_fn)(struct blkcg_policy_data *cpd);
typedef void (blkcg_pol_bind_cpd_fn)(struct blkcg_policy_data *cpd);
typedef struct blkg_policy_data *(blkcg_pol_alloc_pd_fn)(gfp_t gfp,
                                struct request_queue *q, struct blkcg *blkcg);
typedef void (blkcg_pol_init_pd_fn)(struct blkg_policy_data *pd);
typedef void (blkcg_pol_online_pd_fn)(struct blkg_policy_data *pd);
typedef void (blkcg_pol_offline_pd_fn)(struct blkg_policy_data *pd);
typedef void (blkcg_pol_free_pd_fn)(struct blkg_policy_data *pd);
typedef void (blkcg_pol_reset_pd_stats_fn)(struct blkg_policy_data *pd);
typedef size_t (blkcg_pol_stat_pd_fn)(struct blkg_policy_data *pd, char *buf,
                                      size_t size);

struct blkcg_policy {
        int                             plid;
        /* cgroup files for the policy */
        struct cftype                   *dfl_cftypes;
        struct cftype                   *legacy_cftypes;

        /* operations */
        blkcg_pol_alloc_cpd_fn          *cpd_alloc_fn;
        blkcg_pol_init_cpd_fn           *cpd_init_fn;
        blkcg_pol_free_cpd_fn           *cpd_free_fn;
        blkcg_pol_bind_cpd_fn           *cpd_bind_fn;

        blkcg_pol_alloc_pd_fn           *pd_alloc_fn;
        blkcg_pol_init_pd_fn            *pd_init_fn;
        blkcg_pol_online_pd_fn          *pd_online_fn;
        blkcg_pol_offline_pd_fn         *pd_offline_fn;
        blkcg_pol_free_pd_fn            *pd_free_fn;
        blkcg_pol_reset_pd_stats_fn     *pd_reset_stats_fn;
        blkcg_pol_stat_pd_fn            *pd_stat_fn;
};

extern struct blkcg blkcg_root;
extern struct cgroup_subsys_state * const blkcg_root_css;
extern bool blkcg_debug_stats;

struct blkcg_gq *blkg_lookup_slowpath(struct blkcg *blkcg,
                                      struct request_queue *q, bool update_hint);
int blkcg_init_queue(struct request_queue *q);
void blkcg_exit_queue(struct request_queue *q);

/* Blkio controller policy registration */
int blkcg_policy_register(struct blkcg_policy *pol);
void blkcg_policy_unregister(struct blkcg_policy *pol);
int blkcg_activate_policy(struct request_queue *q,
                          const struct blkcg_policy *pol);
void blkcg_deactivate_policy(struct request_queue *q,
                             const struct blkcg_policy *pol);

const char *blkg_dev_name(struct blkcg_gq *blkg);
void blkcg_print_blkgs(struct seq_file *sf, struct blkcg *blkcg,
                       u64 (*prfill)(struct seq_file *,
                                     struct blkg_policy_data *, int),
                       const struct blkcg_policy *pol, int data,
                       bool show_total);
u64 __blkg_prfill_u64(struct seq_file *sf, struct blkg_policy_data *pd, u64 v);

struct blkg_conf_ctx {
        struct block_device             *bdev;
        struct blkcg_gq                 *blkg;
        char                            *body;
};

struct block_device *blkcg_conf_open_bdev(char **inputp);
int blkg_conf_prep(struct blkcg *blkcg, const struct blkcg_policy *pol,
                   char *input, struct blkg_conf_ctx *ctx);
void blkg_conf_finish(struct blkg_conf_ctx *ctx);

/**
 * blkcg_css - find the current css
 *
 * Find the css associated with either the kthread or the current task.
 * This may return a dying css, so it is up to the caller to use tryget logic
 * to confirm it is alive and well.
 */
static inline struct cgroup_subsys_state *blkcg_css(void)
{
        struct cgroup_subsys_state *css;

        css = kthread_blkcg();
        if (css)
                return css;
        return task_css(current, io_cgrp_id);
}

static inline struct blkcg *css_to_blkcg(struct cgroup_subsys_state *css)
{
        return css ? container_of(css, struct blkcg, css) : NULL;
}

/**
 * __bio_blkcg - internal, inconsistent version to get blkcg
 *
 * DO NOT USE.
 * This function is inconsistent and consequently is dangerous to use.  The
 * first part of the function returns a blkcg where a reference is owned by the
 * bio.  This means it does not need to be rcu protected as it cannot go away
 * with the bio owning a reference to it.  However, the latter potentially gets
 * it from task_css().  This can race against task migration and the cgroup
 * dying.  It is also semantically different as it must be called rcu protected
 * and is susceptible to failure when trying to get a reference to it.
 * Therefore, it is not ok to assume that *_get() will always succeed on the
 * blkcg returned here.
 */
static inline struct blkcg *__bio_blkcg(struct bio *bio)
{
        if (bio && bio->bi_blkg)
                return bio->bi_blkg->blkcg;
        return css_to_blkcg(blkcg_css());
}

/**
 * bio_blkcg - grab the blkcg associated with a bio
 * @bio: target bio
 *
 * This returns the blkcg associated with a bio, %NULL if not associated.
 * Callers are expected to either handle %NULL or know association has been
 * done prior to calling this.
 */
static inline struct blkcg *bio_blkcg(struct bio *bio)
{
        if (bio && bio->bi_blkg)
                return bio->bi_blkg->blkcg;
        return NULL;
}

static inline bool blk_cgroup_congested(void)
{
        struct cgroup_subsys_state *css;
        bool ret = false;

        rcu_read_lock();
        css = kthread_blkcg();
        if (!css)
                css = task_css(current, io_cgrp_id);
        while (css) {
                if (atomic_read(&css->cgroup->congestion_count)) {
                        ret = true;
                        break;
                }
                css = css->parent;
        }
        rcu_read_unlock();
        return ret;
}

/**
 * bio_issue_as_root_blkg - see if this bio needs to be issued as root blkg
 * @return: true if this bio needs to be submitted with the root blkg context.
 *
 * In order to avoid priority inversions we sometimes need to issue a bio as if
 * it were attached to the root blkg, and then backcharge to the actual owning
 * blkg.  The idea is we do bio_blkcg() to look up the actual context for the
 * bio and attach the appropriate blkg to the bio.  Then we call this helper and
 * if it is true run with the root blkg for that queue and then do any
 * backcharging to the originating cgroup once the io is complete.
 */
static inline bool bio_issue_as_root_blkg(struct bio *bio)
{
        return (bio->bi_opf & (REQ_META | REQ_SWAP)) != 0;
}

/**
 * blkcg_parent - get the parent of a blkcg
 * @blkcg: blkcg of interest
 *
 * Return the parent blkcg of @blkcg.  Can be called anytime.
 */
static inline struct blkcg *blkcg_parent(struct blkcg *blkcg)
{
        return css_to_blkcg(blkcg->css.parent);
}

/**
 * __blkg_lookup - internal version of blkg_lookup()
 * @blkcg: blkcg of interest
 * @q: request_queue of interest
 * @update_hint: whether to update lookup hint with the result or not
 *
 * This is internal version and shouldn't be used by policy
 * implementations.  Looks up blkgs for the @blkcg - @q pair regardless of
 * @q's bypass state.  If @update_hint is %true, the caller should be
 * holding @q->queue_lock and lookup hint is updated on success.
 */
static inline struct blkcg_gq *__blkg_lookup(struct blkcg *blkcg,
                                             struct request_queue *q,
                                             bool update_hint)
{
        struct blkcg_gq *blkg;

        if (blkcg == &blkcg_root)
                return q->root_blkg;

        blkg = rcu_dereference(blkcg->blkg_hint);
        if (blkg && blkg->q == q)
                return blkg;

        return blkg_lookup_slowpath(blkcg, q, update_hint);
}

/**
 * blkg_lookup - lookup blkg for the specified blkcg - q pair
 * @blkcg: blkcg of interest
 * @q: request_queue of interest
 *
 * Lookup blkg for the @blkcg - @q pair.  This function should be called
 * under RCU read lock.
 */
static inline struct blkcg_gq *blkg_lookup(struct blkcg *blkcg,
                                           struct request_queue *q)
{
        WARN_ON_ONCE(!rcu_read_lock_held());
        return __blkg_lookup(blkcg, q, false);
}

/**
 * blk_queue_root_blkg - return blkg for the (blkcg_root, @q) pair
 * @q: request_queue of interest
 *
 * Lookup blkg for @q at the root level. See also blkg_lookup().
 */
static inline struct blkcg_gq *blk_queue_root_blkg(struct request_queue *q)
{
        return q->root_blkg;
}

/**
 * blkg_to_pdata - get policy private data
 * @blkg: blkg of interest
 * @pol: policy of interest
 *
 * Return pointer to private data associated with the @blkg-@pol pair.
 */
static inline struct blkg_policy_data *blkg_to_pd(struct blkcg_gq *blkg,
                                                  struct blkcg_policy *pol)
{
        return blkg ? blkg->pd[pol->plid] : NULL;
}

static inline struct blkcg_policy_data *blkcg_to_cpd(struct blkcg *blkcg,
                                                     struct blkcg_policy *pol)
{
        return blkcg ? blkcg->cpd[pol->plid] : NULL;
}

/**
 * pdata_to_blkg - get blkg associated with policy private data
 * @pd: policy private data of interest
 *
 * @pd is policy private data.  Determine the blkg it's associated with.
 */
static inline struct blkcg_gq *pd_to_blkg(struct blkg_policy_data *pd)
{
        return pd ? pd->blkg : NULL;
}

static inline struct blkcg *cpd_to_blkcg(struct blkcg_policy_data *cpd)
{
        return cpd ? cpd->blkcg : NULL;
}

extern void blkcg_destroy_blkgs(struct blkcg *blkcg);

/**
 * blkcg_pin_online - pin online state
 * @blkcg: blkcg of interest
 *
 * While pinned, a blkcg is kept online.  This is primarily used to
 * impedance-match blkg and cgwb lifetimes so that blkg doesn't go offline
 * while an associated cgwb is still active.
 */
static inline void blkcg_pin_online(struct blkcg *blkcg)
{
        refcount_inc(&blkcg->online_pin);
}

/**
 * blkcg_unpin_online - unpin online state
 * @blkcg: blkcg of interest
 *
 * This is primarily used to impedance-match blkg and cgwb lifetimes so
 * that blkg doesn't go offline while an associated cgwb is still active.
 * When this count goes to zero, all active cgwbs have finished so the
 * blkcg can continue destruction by calling blkcg_destroy_blkgs().
 */
static inline void blkcg_unpin_online(struct blkcg *blkcg)
{
        do {
                if (!refcount_dec_and_test(&blkcg->online_pin))
                        break;
                blkcg_destroy_blkgs(blkcg);
                blkcg = blkcg_parent(blkcg);
        } while (blkcg);
}

/**
 * blkg_path - format cgroup path of blkg
 * @blkg: blkg of interest
 * @buf: target buffer
 * @buflen: target buffer length
 *
 * Format the path of the cgroup of @blkg into @buf.
 */
static inline int blkg_path(struct blkcg_gq *blkg, char *buf, int buflen)
{
        return cgroup_path(blkg->blkcg->css.cgroup, buf, buflen);
}

/**
 * blkg_get - get a blkg reference
 * @blkg: blkg to get
 *
 * The caller should be holding an existing reference.
 */
static inline void blkg_get(struct blkcg_gq *blkg)
{
        percpu_ref_get(&blkg->refcnt);
}

/**
 * blkg_tryget - try and get a blkg reference
 * @blkg: blkg to get
 *
 * This is for use when doing an RCU lookup of the blkg.  We may be in the midst
 * of freeing this blkg, so we can only use it if the refcnt is not zero.
 */
static inline bool blkg_tryget(struct blkcg_gq *blkg)
{
        return blkg && percpu_ref_tryget(&blkg->refcnt);
}

/**
 * blkg_put - put a blkg reference
 * @blkg: blkg to put
 */
static inline void blkg_put(struct blkcg_gq *blkg)
{
        percpu_ref_put(&blkg->refcnt);
}

/**
 * blkg_for_each_descendant_pre - pre-order walk of a blkg's descendants
 * @d_blkg: loop cursor pointing to the current descendant
 * @pos_css: used for iteration
 * @p_blkg: target blkg to walk descendants of
 *
 * Walk @c_blkg through the descendants of @p_blkg.  Must be used with RCU
 * read locked.  If called under either blkcg or queue lock, the iteration
 * is guaranteed to include all and only online blkgs.  The caller may
 * update @pos_css by calling css_rightmost_descendant() to skip subtree.
 * @p_blkg is included in the iteration and the first node to be visited.
 */
#define blkg_for_each_descendant_pre(d_blkg, pos_css, p_blkg)           \
        css_for_each_descendant_pre((pos_css), &(p_blkg)->blkcg->css)   \
                if (((d_blkg) = __blkg_lookup(css_to_blkcg(pos_css),    \
                                              (p_blkg)->q, false)))

/**
 * blkg_for_each_descendant_post - post-order walk of a blkg's descendants
 * @d_blkg: loop cursor pointing to the current descendant
 * @pos_css: used for iteration
 * @p_blkg: target blkg to walk descendants of
 *
 * Similar to blkg_for_each_descendant_pre() but performs post-order
 * traversal instead.  Synchronization rules are the same.  @p_blkg is
 * included in the iteration and the last node to be visited.
 */
#define blkg_for_each_descendant_post(d_blkg, pos_css, p_blkg)          \
        css_for_each_descendant_post((pos_css), &(p_blkg)->blkcg->css)  \
                if (((d_blkg) = __blkg_lookup(css_to_blkcg(pos_css),    \
                                              (p_blkg)->q, false)))

bool __blkcg_punt_bio_submit(struct bio *bio);

static inline bool blkcg_punt_bio_submit(struct bio *bio)
{
        if (bio->bi_opf & REQ_CGROUP_PUNT)
                return __blkcg_punt_bio_submit(bio);
        else
                return false;
}

static inline void blkcg_bio_issue_init(struct bio *bio)
{
        bio_issue_init(&bio->bi_issue, bio_sectors(bio));
}

static inline void blkcg_use_delay(struct blkcg_gq *blkg)
{
        if (WARN_ON_ONCE(atomic_read(&blkg->use_delay) < 0))
                return;
        if (atomic_add_return(1, &blkg->use_delay) == 1)
                atomic_inc(&blkg->blkcg->css.cgroup->congestion_count);
}

static inline int blkcg_unuse_delay(struct blkcg_gq *blkg)
{
        int old = atomic_read(&blkg->use_delay);

        if (WARN_ON_ONCE(old < 0))
                return 0;
        if (old == 0)
                return 0;

        /*
         * We do this song and dance because we can race with somebody else
         * adding or removing delay.  If we just did an atomic_dec we'd end up
         * negative and we'd already be in trouble.  We need to subtract 1 and
         * then check to see if we were the last delay so we can drop the
         * congestion count on the cgroup.
         */
        while (old) {
                int cur = atomic_cmpxchg(&blkg->use_delay, old, old - 1);
                if (cur == old)
                        break;
                old = cur;
        }

        if (old == 0)
                return 0;
        if (old == 1)
                atomic_dec(&blkg->blkcg->css.cgroup->congestion_count);
        return 1;
}

/**
 * blkcg_set_delay - Enable allocator delay mechanism with the specified delay amount
 * @blkg: target blkg
 * @delay: delay duration in nsecs
 *
 * When enabled with this function, the delay is not decayed and must be
 * explicitly cleared with blkcg_clear_delay(). Must not be mixed with
 * blkcg_[un]use_delay() and blkcg_add_delay() usages.
 */
static inline void blkcg_set_delay(struct blkcg_gq *blkg, u64 delay)
{
        int old = atomic_read(&blkg->use_delay);

        /* We only want 1 person setting the congestion count for this blkg. */
        if (!old && atomic_cmpxchg(&blkg->use_delay, old, -1) == old)
                atomic_inc(&blkg->blkcg->css.cgroup->congestion_count);

        atomic64_set(&blkg->delay_nsec, delay);
}

/**
 * blkcg_clear_delay - Disable allocator delay mechanism
 * @blkg: target blkg
 *
 * Disable use_delay mechanism. See blkcg_set_delay().
 */
static inline void blkcg_clear_delay(struct blkcg_gq *blkg)
{
        int old = atomic_read(&blkg->use_delay);

        /* We only want 1 person clearing the congestion count for this blkg. */
        if (old && atomic_cmpxchg(&blkg->use_delay, old, 0) == old)
                atomic_dec(&blkg->blkcg->css.cgroup->congestion_count);
}

void blk_cgroup_bio_start(struct bio *bio);
void blkcg_add_delay(struct blkcg_gq *blkg, u64 now, u64 delta);
void blkcg_schedule_throttle(struct request_queue *q, bool use_memdelay);
void blkcg_maybe_throttle_current(void);
#else   /* CONFIG_BLK_CGROUP */

struct blkcg {
};

struct blkg_policy_data {
};

struct blkcg_policy_data {
};

struct blkcg_gq {
};

struct blkcg_policy {
};

#define blkcg_root_css  ((struct cgroup_subsys_state *)ERR_PTR(-EINVAL))

static inline void blkcg_maybe_throttle_current(void) { }
static inline bool blk_cgroup_congested(void) { return false; }

#ifdef CONFIG_BLOCK

static inline void blkcg_schedule_throttle(struct request_queue *q, bool use_memdelay) { }

static inline struct blkcg_gq *blkg_lookup(struct blkcg *blkcg, void *key) { return NULL; }
static inline struct blkcg_gq *blk_queue_root_blkg(struct request_queue *q)
{ return NULL; }
static inline int blkcg_init_queue(struct request_queue *q) { return 0; }
static inline void blkcg_exit_queue(struct request_queue *q) { }
static inline int blkcg_policy_register(struct blkcg_policy *pol) { return 0; }
static inline void blkcg_policy_unregister(struct blkcg_policy *pol) { }
static inline int blkcg_activate_policy(struct request_queue *q,
                                        const struct blkcg_policy *pol) { return 0; }
static inline void blkcg_deactivate_policy(struct request_queue *q,
                                           const struct blkcg_policy *pol) { }

static inline struct blkcg *__bio_blkcg(struct bio *bio) { return NULL; }
static inline struct blkcg *bio_blkcg(struct bio *bio) { return NULL; }

static inline struct blkg_policy_data *blkg_to_pd(struct blkcg_gq *blkg,
                                                  struct blkcg_policy *pol) { return NULL; }
static inline struct blkcg_gq *pd_to_blkg(struct blkg_policy_data *pd) { return NULL; }
static inline char *blkg_path(struct blkcg_gq *blkg) { return NULL; }
static inline void blkg_get(struct blkcg_gq *blkg) { }
static inline void blkg_put(struct blkcg_gq *blkg) { }

static inline bool blkcg_punt_bio_submit(struct bio *bio) { return false; }
static inline void blkcg_bio_issue_init(struct bio *bio) { }
static inline void blk_cgroup_bio_start(struct bio *bio) { }

#define blk_queue_for_each_rl(rl, q)    \
        for ((rl) = &(q)->root_rl; (rl); (rl) = NULL)

#endif  /* CONFIG_BLOCK */
#endif  /* CONFIG_BLK_CGROUP */

#ifdef CONFIG_BLK_CGROUP_FC_APPID
/*
 * Sets the fc_app_id field associted to blkcg
 * @app_id: application identifier
 * @cgrp_id: cgroup id
 * @app_id_len: size of application identifier
 */
static inline int blkcg_set_fc_appid(char *app_id, u64 cgrp_id, size_t app_id_len)
{
        struct cgroup *cgrp;
        struct cgroup_subsys_state *css;
        struct blkcg *blkcg;
        int ret  = 0;

        if (app_id_len > FC_APPID_LEN)
                return -EINVAL;

        cgrp = cgroup_get_from_id(cgrp_id);
        if (!cgrp)
                return -ENOENT;
        css = cgroup_get_e_css(cgrp, &io_cgrp_subsys);
        if (!css) {
                ret = -ENOENT;
                goto out_cgrp_put;
        }
        blkcg = css_to_blkcg(css);
        /*
         * There is a slight race condition on setting the appid.
         * Worst case an I/O may not find the right id.
         * This is no different from the I/O we let pass while obtaining
         * the vmid from the fabric.
         * Adding the overhead of a lock is not necessary.
         */
        strlcpy(blkcg->fc_app_id, app_id, app_id_len);
        css_put(css);
out_cgrp_put:
        cgroup_put(cgrp);
        return ret;
}

/**
 * blkcg_get_fc_appid - get the fc app identifier associated with a bio
 * @bio: target bio
 *
 * On success return the fc_app_id, on failure return NULL
 */
static inline char *blkcg_get_fc_appid(struct bio *bio)
{
        if (bio && bio->bi_blkg &&
                (bio->bi_blkg->blkcg->fc_app_id[0] != '\0'))
                return bio->bi_blkg->blkcg->fc_app_id;
        return NULL;
}
#else
static inline int blkcg_set_fc_appid(char *buf, u64 id, size_t len) { return -EINVAL; }
static inline char *blkcg_get_fc_appid(struct bio *bio) { return NULL; }
#endif /*CONFIG_BLK_CGROUP_FC_APPID*/
#endif  /* _BLK_CGROUP_H */